Towing with OD off.

[dodge man]

Something I don't understand is why towing with the OD off is easier on the transmission. Does this also unlock the torque convertor? I know if you tow a heavy load in OD, you can overheat the transmission.

I have rebuilt a 727 torqueflite in a 70 Challenger once, so I have a good idea of what goes on inside a transmission. It seems like it would be easier on the transmission if it was in OD and the torque converter was locked up. The only thing I can think of is maybe the transmission is being overloaded in OD and the bands and/or clutch packs are slipping making the transmission overheat.

 

[deerefan]

Something I don't understand is why towing with the OD off is easier on the transmission. Does this also unlock the torque convertor? I know if you tow a heavy load in OD, you can overheat the transmission.

I have rebuilt a 727 torqueflite in a 70 Challenger once, so I have a good idea of what goes on inside a transmission. It seems like it would be easier on the transmission if it was in OD and the torque converter was locked up. The only thing I can think of is maybe the transmission is being overloaded in OD and the bands and/or clutch packs are slipping making the transmission overheat.

You have the gist of it. In OD, you are dealing with a "lazy" ratio, economical, not towing, based. It also keeps the truck in its minimal powerband. By turning OD off, say on a 4 spd auto, you are keeping the truck in its sweet spot, not building up a ton of heat in the tranny. The truck as a whole will run better and tow better with OD off and your tranny will do a lot less gear hunting, which also increases wear.

 

[Bird]

I always thought it was OK to tow in OD if the load was light enough that the transmission wasn't frequently shifting up and down. If the load is heavy enough and the road hilly enough to cause frequent shifting, then I'd turn off the OD. Is that not the case? I know when I had a 17' aluminum bass boat with a 55 hp outboard, it was light enough that I towed it in OD with my Ford Ranger pickup with the 4.0L V-6 engine.

 

[dave1949]

The '03 automatic 6.0L F250 I had would absolutely scream before shifting - uphill or down - before shifting with OD off and towing. I didn't care for that and could have done a better job with a manual. Uphill was no problem, just hold the throttle at something reasonable. Downhill was another story. Just doesn't seem right to let a diesel run that fast. I would end up turning OD back on til I got to the bottom of a hill sometimes. People would actually turn their heads and look at what was making all the noise.

Maybe it wasn't set up right from the factory? Sold it a couple years back, so it really isn't an issue now
Dave.

 

[Diamondpilot]

I do not have a real good answer for you but I know on a trip we took to Lake Of The Ozarks I had a friend turn the OD on in his Dodge 4x4 with a 360 to try to break 10 mpg. Within ten miles it was boiling out the tranny fluid though the dip stick. He was pulling a 7,500# boat and there were about 6 others traveling with him in a convoy. It made a mess.

I only use OD when I am towing a empty car hauler or boat trailer. The rest of the time its in tow mode.

Chris

 

[Egon]

On my 1996 dodge with the auto transmission with OD engaged the converter locks up at 80 KPH in the fourth or OD gear. With the OD disengaged the converter locks up at 60 KPH but in third gear.

When towing a heavier load in hills the anemic engine will not pull in OD and I have to lock it out. That means at 2300 rpm I'm at about 95 KPH and usually have no problems with the pulling.

 

[wvpolekat]

I never turn the OD off on my 01 F250 unless it is hunting. Believe that is what the owners manual states. I routinely tow 10,000 lbs with OD on and no issues. I have a trans temp gauge and have never seen it go over 200. With 130,000 on it, I don't see any reason to change what I am doing.

 

[Reg]

Something I don't understand is why towing with the OD off is easier on the transmission. Does this also unlock the torque convertor? I know if you tow a heavy load in OD, you can overheat the transmission.

I have rebuilt a 727 torqueflite in a 70 Challenger once, so I have a good idea of what goes on inside a transmission. It seems like it would be easier on the transmission if it was in OD and the torque converter was locked up. The only thing I can think of is maybe the transmission is being overloaded in OD and the bands and/or clutch packs are slipping making the transmission overheat.

Basically it keeps you in a lower gear, by blocking the top (overdrive) gear.
There is less tendency toward "lugging".
The increase in revs for any given road speed also means the cooling fluids in both the rad and trans are pumped at a faster rate, so there is better cooling of both.

"Overdrive" is somewhat of a misnomer these days anyway, since "Top" gear is rarely a "direct" 1:1 ratio.

Tow/Haul mode is a little more complex, and different between manufacturers.
In it's simplest form it raises all the shift points, on some transmissions it also locks out the highest gear, or maybe the two highest gears.
Some just raise all the shift points and O/D doesn't come in until ~55 or above.
In others there is "intelligence" to cause downshifts if the brakes are applied but there is no significant slowing within 1/2 a second or so. Don't ride your brakes on long down grades with these, or you will have very high revs in low gears. Normal upshifting is not restored until you get on the gas again for 1/2 second or so.

 

[carpenter383]

Yes the torque converter clutch (tcc) will still lock in drive (1 to 1 ratio) and even in second gear if you're moving fast enough.
The main reason not to tow in overdrive (aside from shifting back and fourth) is because the overdrive clutch or band typically dosen't have sufficient holding power to keep from slipping under heavy loads. This is especially true in the older o/d trannies. In the newer ones with tow/haul the computer raises line pressure, and shift points which makes it less likley to slip.
A shift correction kit will help an auto tranny survive under heavy duty conditions, They typically address/fix factory issues and common problems and don't necessarilly make the trans shift hard.
Auxillary trans coolers are cheap, easy to install, and should be considered a must have for anyone towing on a regular basis, Heat is the worst enemy.
If you ever get a trans rebuilt that you know is gonna see alot of towing, the builder can install extra clutches, wide bands, bigger servos, stronger hard parts, etc. that will make the trans alot more durable.

 

[Tul01]

Sorry, not trying to hijack the thread, but what about heavy loads in a half ton. My father in law routinely drives with up to 8 hours with 1500-2000lbs in his 07 tundra. I've wondered while driving with him if it should be in tow mode or is this realistically not even similar to what a trailer will cause?

Brent

 

[dodge man]

I always thought the tow mode wasn't really needed with just heavy load in the bed, unless you are in a lot of hills or driving a speed where the tranny is hunting gears.

 

[Diamondpilot]

Yes, 2,000# in the bed of a Tundra is only 1/5th of its rated 10,000# capacity so I would not worry about it. It would be like toting around a empty car hauler.

Chris

 

[Josh61513]

Basically it keeps you in a lower gear, by blocking the top (overdrive) gear.
There is less tendency toward "lugging".
The increase in revs for any given road speed also means the cooling fluids in both the rad and trans are pumped at a faster rate, so there is better cooling of both.

"Overdrive" is somewhat of a misnomer these days anyway, since "Top" gear is rarely a "direct" 1:1 ratio.

Tow/Haul mode is a little more complex, and different between manufacturers.
In it's simplest form it raises all the shift points, on some transmissions it also locks out the highest gear, or maybe the two highest gears.
Some just raise all the shift points and O/D doesn't come in until ~55 or above.
In others there is "intelligence" to cause downshifts if the brakes are applied but there is no significant slowing within 1/2 a second or so. Don't ride your brakes on long down grades with these, or you will have very high revs in low gears. Normal upshifting is not restored until you get on the gas again for 1/2 second or so.

Well put. "Overdrive" is simply any ratio between the engine speed and transmission output speed that is less than 1:1. Some of the higher count automatic transmissions have more than one "overdrive" gear ratios.

Another big contributor to heat generation is an unlocked torque converter. In top gear and a heavy load you will often notice that the transmission will unlock the torque converter to allow the engine to rev slightly higher where it can make more power. This works great as a short term solution, but if you are hauling a load it may stay ulocked for longer periods which can generate a lot of heat energy. If the transmission is locked out of top gear, it will not need to unlock the torque converter nearly as often because the engine is already revving higher where it can make more power.

Also, the clutch packs which are used for top gear are sometimes marginal in strength, ie GM 4L60 transmissions. When high inertia (high GCWR) shifts from 3rd into 4th are made it wears the 3-4 clutch packs significantly. This is also avoided by locking out 4th gear ("overdrive").

Using a "tow/haul" mode often influences the lockup strategy of the torque converter, another reason to use it when appropriate.

 

[KeithInSpace]

My approach is pretty simple: If the torque converter is dropping out of "lock", you need to choose a lower gear. My Expedition only has 4 speeds, so this means nearly 100% of my towing is done at over 3,000 RPM on the interstate. Oddly, I get considerably better mileage doing this than I do trying to use overdrive.

In short, if you're out of lock-up, there is nothing left to happen but for the fluid to cook.

That said, my truck doesn't have a "tow" mode, as it differs from the "O/D OFF" button. Perhaps that would help around town, but I'd still be weary on the interstate.

 

[Highbeam]

Always tow in OD unless your trans "hunts" by shifting gears and/or unlocking and relocking the torques converter. In addition, always monitor trans fluid temps with an actual gauge and not the in-dash garbage put out by the automakers.

Even with my big huge 7.3 diesel engine, I am not afraid to turn off O/D and let the rpms pick up when needed. Pretty much anything but flat interstate finds me manually engaging and disengaging O/D. There's no penalty for using the O/D button to "shift" in and out of O/D as conditions allow, just don't do it so often that you are manually hunting.

Happiness is a huge aftermarket atf cooler, a gauge to monitor temps, a nice big tractor on the trailer, a cup of coffee, and a field of tall grass that needs mowing 50 miles away.

 

[flusher]

Happiness is a huge aftermarket atf cooler, a gauge to monitor temps, a nice big tractor on the trailer, a cup of coffee, and a field of tall grass that needs mowing 50 miles away.

Yep--sounds like a little bit o' heaven.

 

[20 20]

WHAT DOES THE MANUAL SAY?

Towing a heavy load in OD will cause issues, maybe not right away but it will happen. It has a tow mode for a reason why not use it the way it is intended?

 

[dodge man]

I have a tow mode and a OD off mode on my 2007 Dodge. I think the tow mode just rasise the shift points while the OD off mode holds it out of 4th and 5th gear, but I'm not sure.

 

[firefighter jim]

When in Tow/Haul mode, should you keep gear selector in OD with a heavy load? Or 3rd? (GMC 4 speed automatic)

 

[grunewald]

I have a tow mode and a OD off mode on my 2007 Dodge. I think the tow mode just rasise the shift points while the OD off mode holds it out of 4th and 5th gear, but I'm not sure.

Have 2007.5 Dodge Diesel, 6-speed auto. Tow/haul mode upshifts faster, but still will go into overdrive. I use the manual shift, which can be set from 1 thru 6 speeds, 6 being overdrive. By setting it to 5, it will not shift past 5 gear. I'm guessing your truck is not 6-speed? Different trans.?